Thermostatically controlled bath



Patented Aug. 30, 1949 THERMOSTATICALLY CONTROLLED BATH Charles C. Hulhert, Cabin Creek, W. Va., assignor to The Pure Oil Company, Chicago, 111., a corporation of Ohio Application June 1, 1946, Serial No. 673,729

6 Claims. 1

This invention relates to method and apparatus for controlling the temperature of thermal baths and heating mediums. Although invention is particularly directed to control of liquid baths in which a mercury-expansion type of thermoregulator is employed, it is not limited thereto, but is useful in connection with the control of temperature of fluid heating mediums in general in which a thermostatic control device is used to maintain a predetermined temperature.

The use of thermoregulators or thermostatic control devices in conjunction with electric heating elements are well known for maintaining the temperature of a heating bath or fluid constant. Apparatus for maintaining a constant temperature thermal bath by means of a mercury-expan sion type thermoregulator is disclosed in Patent No. 2,037,993. However, when using a device of the type shown in the aforesaid patent fluctuations of plus and minus 0.1 or more from the desired temperature are obtained.

I have discovered that if a low wattage source of radiant energy is placed contiguous to the thermoregulator in an apparatus of the type described in the aforesaid patent temperature variation from the desired temperature of not more than plus or minus 0.01 F. may be obtained.

An object of the invention is to provide a method for substantially eliminating temperature variations encountered in thermostatically controlled heating baths.

Another object of the invention is to provide apparatus for maintaining thermal baths and heating fluids at a substantially constant temperature.

, Other objects of the invention will become apparent from the following description and. the accompanying drawing, of which Figure l is a diagrammatic elevational view illustrating one form of the invention, and Figure 2 is a Wiring diagram illustrating the manner in which the elements shown in Figure 1 are connected.

Referring to the drawings the numeral indicates a low wattage incandescent tubular-shaped lamp. This lamp may be a 25 watt lamp and is designed to provide a small amount of radiant heat energy as compared to the heating elements in the liquid bath. The lamp 1' is preferably surrounded by a cylindrical shield 2 made of metal or other opaque material which is open directly opposite the mercury-type thermoregulator 3, in order to permit the radiant energy of lamp to impinge upon the regulator. The shield 2 is placed around the lamp I in order to prevent the lamp affecting the thermometer used to indicate bath temperature, or other objects or materials, such as viscosity pipettes, which are to be maintained at bath temperature. The lamp 1 and the thermoregulator 3 are immersed in a vessel 4 which contains oil or other liquid, the temperature of which is to be regulated. Where the vessel 4 is made of glass or other transparent material the lamp I may be placed outside the vessel but in close proximity to the thermoregulator.

The lamp I and shield 2 are adapted to be held in a socket 5 adapted to be supported in the elongated slot 5 of the mounting block 1 above the vessel 4. The socket 5 is preferably provided with grooves 5' on opposite sides thereof to permit the socket to slide back and forth in the slot 5. A cap 8 is screwably mounted on the top of socket 5. The base of the cap 8 is flat and of a greater diameter than the width of the slot 6. By unloosening the cap 8 the socket 5, together with the lamp I and shield 2, may he slid in notch 5 toward or away from the thermoregulator 3. and by screwing the cap 8 tightly the lamp is held firmly at the desired position. The mounting block 1 may be either supported on the top of vessel 4 or may be independently supported above the vessel by means of a suitable stand and bracket (not shown).

Thermoregulator 3 is also supported by the mounting block I. The thermoregulator 3 is of the conventional type containing a column of mercury 9, wires 10 and II, one slightly above the other, extending into the space I! in order to contact the mercury column when it expands. The wires Ill and II are connected by means of binding posts [3 and I4 to wires 15 and 16 which in turn are connected to a suitable source of electric current I 'l, which may be one or more dry cells, and to a relay coil I1, connected in series.

The distance between the lamp l and the thermoregulator 3 is small and will depend somewhat on the size of the lamp. When using a 25 watt lamp 9. distance less than one inch gives satisfactory results. Greater distances are preferable with higher wattage lamps. By providing means for sliding the lamp toward and away from the thermoregulator 3 the proper distance to give the optimum temperature regulation can be found and the lamp set in the proper position.

Located in the oil bath in the vessel 4 is an intermittent electric heater l8. The intermittent heater T8 is connected to a source of electric current 20, which may be either A. C. or D. C., through the spring controlled relay switch 2|.

3 Lamp i is connected in parallel with the intermittent heater is through relay switch it to the source of electric current. The relay switch 2! is adapted to be held in open position by the relay when it is energized by current flowing through coil from the battery, or other source of supply i'i. Current will flow through the coil i? and energize the relay" 22only when the temperature of the bath has risen to the desired point, thereby causing the column of mercury in the thermoregulator 3 to expand and make contact with the wires ii] and II. energized. it will pull the switch. 21 open, thereby breaking the circuit through. lamp ii and heater.

Hi. When the temperature in the bath drops below a predetermined point the mercury in the thermoregulator contracts breaking the circuit, thereby closing the switch 2! and causing current to flow through the heater I8 and lamp l.

Connected tov the. same source of current as I the intermittent heater [8 but-in parallel therewith is the continuous heater 23. The heater 2-3 is connected to'anautot'ransformer. in order to enable the heat output ofiheater 23 to bc ied, depending on the temperature whichit is desired. to. maintain in. the. bath. The heater 23 upon closing, the main circuit switch 25 will be ed on a suitable bracket adjacent the thermorcgulator 3. It will be understood that in order to use lamp 25, a. transparent Vessel 4 must be used.

An electrically operated stirrer may be provided to keep the bath in a constant state of agitation. 7

In operation, upon closing the main switch heater 23. will go into operation, as well as intermittent heater l8 since the switch 2i will be closed. Lamps i and '25 will also be lighted.

' The capacity of theheaterzd is such that it will.

heat the bath to'a temperature a few degrees below the temperature which it is desired to tain. The intermittent heater 98 su plies the required additional heat to bring the tempera ture of the bath to the desired level; bath reaches the desired temperature the mercury in the thermoregulat'orwill expand and close the circuit through the coil ll, thereby energizing relay 22, opening switch 2| and cutting the intermittent heater iB' and'lamp l out of the circuit.

When the temperature in the bath falls below the desired level the circuit through coil l1 will opendeenergizing relay 22 and permitting the spring controlled switch 2! to close; thereby closing the lamp 5 and intermittent heater is circuit. Because of'the proximity of thelamp l to the thermoregulator' 3 the mercury therein will be heated more rapidly than it would be due merely to the temperature of the bath, thereby causing the circuit through coil IT to close, and cutting the heater !8' out of the circuit before the bath rises above the temperature it is'desired' to maintainin the bath. Thus the lamp I eliminates or greatly reduces the time lag ordinarilyexperienced'loetweenthe time th bath reaches the When the relay 22 becomes When the desired temperature and the time the thermoregulator opens the heating circuit. The more closely the lamp l is located to the thermoregulator 3 the shorter will b the heating phase of the temperature cycle by the heater l8 and hence the shorter will be the complete temperature cycle, and with. a resultant smaller variation in temperature of the bath;

In actual operation, whereas before installation of the lamp 1 it was not possible to maintain the temperature of a 3 gallon oil bath plus or minus 0110?" to 0.20. F., after installation of the lamp l the variation in temperature of a 100 F. bath could. be held to :0..01 F. and the variation temperature of a 120 or 210 F. bath could be held to $0.02? F. with a complete temperature cycle; i. e. the period from the time the heater [8. circuit is closed, then opened and again closed, of 60 seconds. In theseitests the lamp I was a 25 Watt incandescent lamp and was located. a distamcebetween one-half and one inch from the mercury thermoregulator'.

In order to provide a' simple means of making fine adjustments in the temperature ofth bath which normally involve changing the volume of mercury in the thermoregulat'or, the lamp 26 is provided. Lamp 20 canbe. moved toward and away from the thermoregulator 3 depending on the temperature regulation: required. By moving the lamp 26 closer to the thermoregulator'the' mercury in the thermoregulator is maintained at a higher-temperature, thus causing an increase in volume of merucury in the regulator; The net effect is to cause a slightly-lower temperature in the bath because a; lower temperature is required to expand the mercury sufiiciently to close the thermoregulator circuit.

Likewise, moving the lamp further away from the thermoregulator 3 produces a lowertemperature of the mercury in the thermoregulator; causing it to contract'somewhat and requiring a higher temperatur to close the th-ermoregulator circuit. As previously pointed out an opaque shield open only directly opposite'the thermoregulator 3 may be placed-around the lamp 26in order to permit the thermoregul'ator' to be exposed to the radiant energy while preventing it from afiecting other objects in its vicinity.

Although I have illustrated and described the "invention particularly in relation to the control of liquid baths using a mercury-type thermoregulator, it is to be-understood that the temperature of a vaporous or gaseous heating means or bath can be controlled in the samemanner, and that any thermostatic control device, such as a thermocouple, may be used in place of the thermoregulator.

It is claimed:

1. Apparatus for maintaining the temperature of a fluid heating medium comprising an electric heating element, a second electric heating element connected in parallel with said first mentioned element both of which are adapted to be immersed in said medium, a liquid expansion thermostatic control device adapted to open and close the circuit of said second electric heating element at predetermined temperature adapted to be immersed in said medium, and a source of radiant energy of low output as compared to the output of said second electric heating element, adapted to go on and ed simultaneously with said second electric heating element, adjacent to said thermostatic control device and to which said control deviceis intermittently exposed.

2. Apparatus in accordance with claim I- in which the source of radiant energi is connected in parallel with said second electric heating element.

3. Apparatus in accordance with claim 1 in which the thermostatic control device is a mercury-type thermoregulator.

4. Apparatus in accordance with claim 1 including means for varying the distance between said source of radiant energy and said thermostatic control device.

5. A temperature controlled liquid bath apparatus comprising, a transparent vessel for containing said liquid, an immersion type mercury expansion thermoregulator in said liquid, an electric heating element immersed in said liquid and connected in circuit to be opened and closed by said thermoregulator, a source of radiant energy of low output relative to said electric heating element immersed in said bath close to said thermoregulator, said source of radiant energy being connected in parallel with said heating element, a second electric heating element immersed in said bath and being connected in circuit to operate independently of said firstmentioned heating element, a second source of radiant energy of higher output than said firstmentioned source of radiant energy disposed 6 outside said vessel contiguous to said thermoregulator and means to vary the distance between said thermoregulator and said second source of radiant energy.

6. The apparatus in accordance with claim 5 including means for varying the distance between the thermoregulator and said first-mentioned source of radiant energy.

CHARLES C. HULBERT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,165,958 Freas Dec. 28, 1915 1,186,024 Mulvany June 6, 1916 1,235,796 Harvey Aug. 7, 1917 1,572,990 Colby Feb. 16, 1926 1,606,858 Wilhjem Nov. 16, 1926 1,680,398 Thomas Aug. 14, 1928 1,873,421 Kanter Aug. 23, 1932 2,007,596 Burke July 9, 1935 2,037,993 Miller et a]. Apr. 21, 1936 2,145,722 Hall Jan. 31, 1939 2,400,735 Bradford May 21, 1946 

